JP6938838B2 - Polyimide film with improved thermal conductivity and its manufacturing method - Google Patents

Description

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0017561 dated February 13, 2018 and Korean Patent Application No. 10-2019-00000955 dated January 2, 2019. Any content disclosed in the literature of the application is included as part of this specification.

The present invention relates to a polyimide film having improved thermal conductivity and a method for producing the same.

Polyimide (PI) is a polymer with a relatively low crystallinity or a nearly amorphous structure, which is easy to synthesize, can form a thin film, and is a cross-linking group for curing. It is a polymer material that has excellent heat resistance and chemical resistance, excellent mechanical properties, electrical properties and dimensional stability due to its transparency and rigid chain structure. Currently, it is widely used as an electric and electronic material such as automobiles, aerospace fields, flexible circuit boards, liquid crystal alignment films for LCDs, adhesives and coating agents.

In particular, polyimide is a high-performance polymer material having high thermal stability, mechanical properties, chemical resistance, and electrical properties, and interest is increasing as a substrate material for flexible displays. In order to use it for display applications, it must be transparent, and in order to reduce the defective rate due to residual stress of the substrate in the heat treatment process for manufacturing displays, the coefficient of thermal expansion is negative at a temperature of 350 ° C or higher. There is a problem that shouldn't be there. Therefore, many studies are currently underway to minimize the optical properties and thermal history changes while preserving the basic properties of polyimide.

Flexible displays are in increasing demand in the market due to their flexible form factor, light and thin properties and unbreakable properties. In embodying such a flexible display, a polyimide composed of BPDA (3,3', 4,4'-Biffeneylterracarboxylic diamine) -PDA (phenylene diamine), which is a polyimide having excellent heat resistance, is used.

A flexible display element, for example, a TFT element, is manufactured by forming a multilayer inorganic film such as a buffer layer, an active layer, and a gate insulator on a cured polyimide. ..

Recently, when the OLED type flexible display is realized, the polyimide substrate has an issue that is more vulnerable to afterimages than the glass substrate. It is presumed that the cause of the afterimage is the difference in brightness that appears due to different currents at the same voltage due to the shift (shift) _{of the threshold voltage (Vth) in the current-driven OLED display.} Here, the threshold voltage (Threshold Voltage: _Vth ) means the critical point of the voltage at which the current flow starts to flow through the channel, and the threshold voltage is in a state where the current that did not flow on the MOSFET flows. The potential barrier at the time of inversion.

The present inventors have found during research to solve the afterimage problem that the _Vth shift is further deepened by the heat generated when the TFT is driven.

In order to solve the above problems, the present invention is to provide a polyimide film capable of improving heat dissipation characteristics, that is, thermal conductivity and thermal diffusivity, _{and mitigating a Vth shift.}

The present invention also provides a method for producing the polyimide film.

The present invention also provides a flexible display element containing the polyimide film as a substrate.

In order to solve the above-mentioned problems, the present invention provides a polyimide film containing an imide monomolecular compound as an organic filler and having a thermal conductivity (k) of 0.2 W / m · K or more as defined by the following formula 1. offer.
[Formula 1]
Thermal conductivity (k) = specific heat (C) x density (ρ) x thermal diffusivity (α)
In the above formula, C, ρ and α represent the specific heat (J / g · K), density (g / cm ³ ) and thermal diffusivity (mm ² / sec) of the polyimide film, respectively.

［化学式２］

前記式において、Ｘ、Ｙ、Ｘ_１及びＹ_１は、炭素数６〜１２の単環または多環芳香族環または複数個の単環芳香族環が連結された有機基である。 According to one example, the imide monomolecular compound can be one or more compounds selected from the compounds of Chemical Formula 1 and Chemical Formula 2 below.
[Chemical formula 1]

[Chemical formula 2]

In the above formula, X, Y, X ₁ and Y ₁ are organic groups in which a monocyclic or polycyclic aromatic ring having 6 to 12 carbon atoms or a plurality of monocyclic aromatic rings are linked.

According to one example, the polyimide film contains 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 4,4'-para-phenylenediamine (pPDA) as polymerization components. It is a thing.

［化学式４］

。 According to one embodiment, the compound of Chemical Formula 1 or Chemical Formula 2 can be a compound of Chemical Formula 3 or Chemical Formula 4 below.
[Chemical formula 3]

[Chemical formula 4]

..

According to one example, the mol ratio of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 4,4'-para-phenylenediamine (pPDA) is 0.98 :. It is 1 to 0.99: 1.

According to one embodiment, the polyimide film has a specific heat of 1.5 J / g · K or more, a density of 1.5 g / cm ³ or more, and a thermal diffusivity of 0.07 mm ² / sec or more measured at a thickness of 10 μm. There is.

According to another aspect of the present invention, the polymerization solution is 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) with respect to 1 mol of 4,4'-paraphenylenediamine (pPDA). A step of producing a polyimide precursor by adding a polymerization component contained in less than 1 mol; a step of adding an imide monomolecular compound as an organic filler to the polyimide precursor solution; a step of applying the polyimide precursor solution on a substrate; and Provided is a method for producing a polyimide film, which comprises a step of drying and heating the applied polyimide precursor solution.

According to one embodiment, the final curing temperature can be 450 ° C. or higher in the curing step through drying and heating of the polyimide precursor solution.

According to one example, the imide monomolecular compound is one or more selected from the compounds of the chemical formula 1 and the chemical formula 2, and the compound of the chemical formula 1 or the chemical formula 2 is 0. It is contained in 1 to 10% by weight.

According to another aspect of the present invention, there is provided a flexible display device containing the above-mentioned polyimide film as a substrate.

According to the present invention, a monomer is introduced into a polyamic acid composition which is a polyimide precursor to improve the density, specific heat, thermal diffusivity, etc. of the polymer in the plane direction during high temperature curing. Thermal conductivity, that is, heat dissipation characteristics can be improved. Improving the heat dissipation characteristics of the film can alleviate the threshold voltage shift phenomenon of the current-driven display, and can greatly improve the afterimage characteristics of the display.

It is a drawing explaining the method of measuring the degree of thermal diffusivity. It is a drawing explaining the method of measuring the degree of thermal diffusivity. The polymer behavior is schematically illustrated when the compositions according to Comparative Examples (a) and (b) are applied to a glass substrate and cured. It is a photograph of a measuring device of thermal diffusivity. It is a sample photograph used for measuring the degree of thermal diffusivity.

Since the present invention can be subjected to various transformations and have various examples, specific examples will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the invention to any particular embodiment and must be understood to include any transformations, equivalents or alternatives within the ideas and technical scope of the invention. It doesn't become. In explaining the present invention, if it is determined that a specific description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

The present invention relates to a polyimide film for manufacturing a flexible substrate, which can improve the afterimage characteristics of a display by controlling the heat dissipation characteristics of a plastic substrate.

Specifically, the present invention provides a polyimide film having a thermal conductivity (k) of 0.2 W / m · K or more as defined by the following mathematical formula 1.
[Formula 1]
Thermal conductivity (k) = C × ρ × α
In the above formula 1, C, ρ and α represent the specific heat (J / g · K), density (g / cm ³ ) and thermal diffusivity (mm ² / sec) of the polyimide film, respectively.

According to the preferred embodiment, the thermal conductivity can be 0.25 W / m · K or higher. The larger the thermal conductivity of the film, the better the heat dissipation characteristics. Therefore, if the heat dissipation characteristics are improved, the current fluctuation due to the shift of the _{threshold voltage (Vth) is suppressed.} Thereby, the afterimage characteristic of the display element can be improved.

When an inorganic filler is used to improve the heat dissipation characteristics of the film, the thermal conductivity is excellent, but since the inorganic filler has a high affinity for moisture, the hygroscopicity of the film causes VHR (voltage holding ratio). The characteristics become poor.

Therefore, in the present invention, an organic single molecule that is not an inorganic filler is used as the organic filler in order to improve the heat dissipation characteristics of the film. As a result, a polyimide film having improved thermal conductivity was obtained while complementing other physical characteristics required for the flexible display element.

The thermal conductivity (k) of the polyimide film is obtained from the product of the specific heat, density and thermal diffusivity of the polyimide film.

The specific heat (J / g · K) of the polyimide film can be measured by the DSC method, and the density (g / cm ³ ) can be measured by the Archimedes method.

The thermal diffusivity of the polyimide film can be determined by the laser flash method using ASTM E1461.

1 and 2 schematically show a method of measuring the degree of thermal diffusivity by the flash method. When a film sample of a predetermined thickness is irradiated with a heat source of a flash source, a detector detects the temperature over time to obtain a Tt graph as shown in FIG. 2, and here, Tt. The degree of thermal diffusivity can be obtained by finding the _{time t 1/2 at} which T in the graph becomes 1/2 and substituting it into Equation 2. Equation 2 is the PARKER's equation, which is calculated as a function of sample thickness and time, assuming that the material is thermally isotropic with no thermal loss. The method. In the Parker equation of FIG. 2, L is the thickness of the sample and α is the degree of thermal diffusivity.

［化学式２］

前記式において、Ｘ、Ｙ、Ｘ_１及びＹ_１は、炭素数６〜１２の単環または多環芳香族環または複数個の単環芳香族環が連結された有機基である。 According to one embodiment, the polyimide film contains 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 4,4'-paraphenylenediamine (pPDA) as polymerization components. It is obtained by polymerizing and curing a composition containing the compound of the following chemical formula 1 or chemical formula 2.
[Chemical formula 1]

[Chemical formula 2]

In the above formula, X, Y, X ₁ and Y ₁ are organic groups in which a monocyclic or polycyclic aromatic ring having 6 to 12 carbon atoms or a plurality of monocyclic aromatic rings are linked.

［反応式２］

The monomolecular compound of Chemical Formula 1 or Chemical Formula 2 can be produced by the method according to Reaction Scheme 1 or Reaction Scheme 2 below.
[Reaction formula 1]

[Reaction equation 2]

［化学式４］

。 According to a preferred embodiment, the compound of Chemical Formula 1 or Chemical Formula 2 comprises a compound of Chemical Formula 3 or Chemical Formula 4 below.
[Chemical formula 3]

[Chemical formula 4]

..

According to one example, the mol ratio of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 4,4'-para-phenylenediamine (pPDA) is 0.98 :. It is 1 to 0.99: 1.

According to one embodiment, the polyimide film has a specific heat of 1.5 J / g · K or more, a density of 1.5 g / cm ³ or more, and a thermal diffusivity of 0.07 mm ² / sec or more measured at a thickness of 10 μm. There is. More preferably, the specific heat may be 1.7 J / g · K or more, the density ^{may be 1.7 g / cm 3} or more, and the thermal diffusivity may be 0.08 mm ² / sec or more. Such properties are such that the thermal conductivity is improved by 2 times or more, preferably 2.5 times or more, as compared with the case where the monomolecular compound is not contained.

According to another aspect of the present invention, the polymerization solution is 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) with respect to 1 mol of 4,4'-paraphenylenediamine (pPDA). A step of producing a polyimide precursor by adding a polymerization component contained in less than 1 mol; a step of adding a monomer of the chemical formula 1 or the chemical formula 2 to the polyimide precursor solution; a step of applying the polyimide precursor solution on a substrate; A method for producing a polyimide film comprising the steps of drying and heating the applied polyimide precursor solution;

According to one embodiment, the final curing temperature can be 450 ° C. or higher in the curing step through drying and heating of the polyimide precursor solution.

According to one embodiment, the compound of Chemical Formula 1 or Chemical Formula 2 is contained in an amount of 5 to 50% by weight, preferably 15 to 25% by weight, based on the total weight of the precursor solution. If the content of the monomolecular compound is excessively small, the effect of improving the thermal conductivity of the film is minute, and if the content of the monomolecular compound is excessively large, the film forming characteristics are deteriorated and the transparency is lowered. ..

The composition according to the present invention improves the thickness and the density in the plane direction of the polymer (PAA, PI) film at the time of high-temperature curing by introducing the compound of Chemical Formula 1 or Chemical Formula 2, and reduces specific heat and the like. Can be improved.

FIG. 3 shows the polymer behavior as the curing progresses after the composition (a) containing no imide single molecule and the composition (b) containing an imide single molecule according to the present invention are applied to a glass substrate. While the polyamic acid structurally changes to polyimide, the imide-structured monomolecular compound interacts with the surrounding macromolecules, which means an increase in π-π interactivity, which means the thermal diffusivity and thermal conductivity of the film. Contributes to improving the degree.

The polyimide film according to the present invention has a positive coefficient of thermal expansion at a temperature of 350 ° C. or higher. More specifically, in a CTE measurement method using TMA, a polyimide film cooled after a primary temperature rise is used. When the secondary temperature is raised from 100 ° C. to 460 ° C., the measured CTE value shows a positive value at a temperature of 350 ° C. or higher, preferably having a value of 0 or more and 15 ppm / ° C. or lower, and preferably. It has a coefficient of thermal expansion of 0 or more and 10 ppm / ° C. or less.

The polyimide precursor polymerization reaction is carried out by a usual polyimide precursor polymerization method such as solution polymerization.

The reaction is carried out under anhydrous conditions, and the temperature during the polymerization reaction is −75 to 50 ° C., preferably 0 to 40 ° C. The method was carried out by adding an acid dianhydride in a state where the diamine was dissolved in an organic solvent. Among them, the diamine and the acid dianhydride were contained in the polymerization solvent in a content of about 10 to 30% by weight, and the polymerization time and reaction were carried out. The molecular weight is regulated by the temperature.

Specific examples of the organic solvent used in the polymerization reaction include γ-butyrolactone, 1,3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, and 4-hydroxy-4-methyl-2-pentanone. Ketones such as; aromatic hydrocarbons such as toluene, xylene, tetramethylbenzene; ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene Glycol ethers (cellosolve) such as glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol diethyl ether, triethylene glycol monoethyl ether; ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, Diethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethanol, propanol, ethylene glycol, propylene glycol, carbitol, dimethylacetamide (DMAc), N, N-diethylacetamide, dimethylformamide (DMF), diethylformamide (DEF) , N, N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N-vinylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, N, N-dimethylmethoxy Acetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylurea, N-methylcaprolactam, tetrahydrofuran, m-dioxane, P-dioxane, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether , 1,2-Bis (2-methoxyethoxy) ethane, bis [2- (2-methoxyethoxy)] ether, and mixtures thereof are selected from the group.

Desirably, sulfoxide-based solvents such as dimethyl sulfoxide and diethyl sulfoxide; formamide-based solvents such as N, N-dimethylformamide and N, N-diethylformamide; acetamide-based solvents such as N, N-dimethylacetamide and N, N-diethylacetamide. Solvent: Pyrrolidone-based solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone are used alone or as a mixture. However, it is not limited to this. In addition, aromatic hydrocarbons such as xylene and toluene are further contained and used.

In the method of producing a polyimide film using the produced polyimide precursor, a polyimide precursor composition containing the polyimide precursor and an organic solvent is applied to one surface of a substrate, and separated from the substrate after an imidization and curing step. Including the stage to do.

Specifically, the polyimide precursor composition is in the form of a solution in which the polyimide precursor is dissolved in an organic solvent, and has such a form, for example, when the polyimide precursor is synthesized in an organic solvent. The polyimide precursor composition may be obtained by further adding itself or the same solution of the polyimide precursor solution obtained after the polymerization, or the polyimide precursor solution obtained after the polymerization. It may be diluted with another solvent.

It is desirable that the polyimide precursor composition contains a solid content in an amount that gives an appropriate viscosity in consideration of processability such as coatability in the film forming step, and the solid content is the total amount of the polyimide precursor composition. It can be contained in 5 to 20% by weight based on the weight. Alternatively, it is desirable to adjust the polyimide precursor composition so that it has a viscosity of 400 to 50,000 cP. When the viscosity of the polyimide precursor composition is less than 400 cP and the viscosity of the polyimide precursor composition exceeds 50,000 cP, the fluidity is lowered during the production of the display substrate using the polyimide precursor composition. , It may cause problems in the manufacturing process such as not being applied uniformly at the time of coating.

Next, the polyimide precursor composition produced above is applied to one surface of a substrate, thermally imidized and cured at a temperature of 80 to 500 ° C., and then separated from the substrate to produce a polyimide film.

At this time, as the substrate, a glass, a metal substrate, a plastic substrate, or the like is used without particular limitation, and among them, among the imidization and curing steps for the polyimide precursor, the substrate is excellent in thermal and chemical stability, and is separately provided. It is desirable to use a glass substrate that can be easily separated from the formed polyimide-based film after curing without damage even without the release agent treatment.

Further, the coating step is carried out by a normal coating method, and specifically, a spin coating method, a bar coating method, a roll coating method, an air knife method, a gravure method, a reverse roll method, a kiss roll method, a doctor blade method, and a spray. A method, a dipping method, a brush method, etc. may be used. Among them, it is more preferable to carry out by a casting method capable of a continuous step and increasing the imidization rate of the polyimide.

In addition, the polyimide precursor composition can be applied to a polyimide film finally produced on the substrate in a thickness range having a thickness suitable for a display substrate.

Specifically, it can be applied in an amount having a thickness of 10 to 30 μm. After applying the polyimide precursor composition, a drying step for removing the solvent present in the polyimide precursor composition is selectively further carried out prior to the curing step.

The drying step is carried out by a usual method, and specifically, is carried out at a temperature of 140 ° C. or lower, or 80 to 140 ° C. If the temperature at which the drying step is carried out is less than 80 ° C., the drying step becomes long, and if it exceeds 140 ° C., imidization proceeds rapidly, making it difficult to form a polyimide film having a uniform thickness.

Subsequently, the curing step can proceed by heat treatment at a temperature of 80-500 ° C. The curing step can also proceed by a multi-step heat treatment at various temperatures within the temperature range. Further, during the curing step, the curing time is not particularly limited, and is carried out for 3 to 60 minutes as an example.

Further, after the curing step, a subsequent heat treatment step can be selectively further carried out in order to increase the imidization rate of the polyimide in the polyimide film and form the polyimide-based film having the above-mentioned physical characteristics. ..

It is desirable that the subsequent heat treatment step be carried out at 200 ° C. or higher, or 200 to 500 ° C. for 1 to 30 minutes. Further, the subsequent heat treatment step may be carried out once, or may be carried out twice or more in multiple steps. Specifically, it is carried out in three stages including a first heat treatment at 200 to 220 ° C., a second heat treatment at 300 to 380 ° C., and a third heat treatment at 400 to 500 ° C., preferably having a final curing temperature of 450. It can be manufactured by curing for 30 minutes or more under the condition of ° C. or higher.

After that, the polyimide film can be produced by peeling the polyimide film formed on the substrate from the substrate by a usual method.

The polyimide according to the present invention has a glass transition temperature of about 360 ° C. or higher. In order to have such excellent heat resistance, the film containing the polyimide can maintain excellent heat resistance and mechanical properties even with respect to high temperature heat added during the device manufacturing process.

The polyimide film according to the present invention can have a thermal decomposition temperature (Td 1%) showing a mass loss of 1% of 550 ° C. or higher.

Further, the polyimide film according to the present invention has very excellent mechanical properties, for example, the elongation is 10% or more, preferably 20% or more, and the tensile strength is 400 MPa or more, preferably 450 MPa. As described above, more preferably, it is 500 MPa or more, and the tensile modulus (Tensile Modulus) can be 10 GPa or more.

The polyimide according to the present invention is used for element substrates, display cover substrates, optical films, IC (integrated circuit) packages, adhesive films, multilayer FPCs (flexible printed circuits), tapes, touch panels, and optical disks. Used in various fields such as protective films.

The present invention provides a flexible display device including the polyimide film. For example, the display device includes a liquid crystal display device (liquid crystal display device, LCD), an organic light emitting device, an organic light emitting diode (OLED), and the like, and in particular, a LTPS (low temperature primary radio) that requires a high temperature process. Suitable for, but not limited to, OLED devices that use the process.

Hereinafter, examples of the present invention will be described in detail so that those skilled in the art can easily carry out the invention. However, the present invention can be embodied in a variety of different forms and is not limited to the examples described herein.

。 <Production Example 1> Synthesis of the compound of Chemical Formula 3 After filling 80 g of the organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, aniline 18 is maintained at a reactor temperature of 25 ° C. .99 g (0.204 mol) was dissolved. To the aniline solution, 30.0 g (0.102 mol) of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 93.7 g of NMP were added at the same temperature and dissolved for a certain period of time. After stirring while stirring, the compound of Chemical Formula 3 was synthesized.
[Chemical formula 3]

..

<Example 1> BPDA-pPDA / Compound of chemical formula 3 (98.9: 100: 2.2) Polyimide polymerization After filling 100 g of the organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows. 6.192 g (57.259 mmol) of para-phenylenediamine (p-PDA) was dissolved while maintaining the temperature of the reactor at 25 ° C. 16.661 g (56.629 mmol) of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 56.96 g of NMP were added to the p-PDA solution at the same temperature to maintain a constant value. After stirring while dissolving for a time, the polyamic acid was polymerized.

After that, 2 wt% of the compound of Chemical Formula 3 produced in Production Example 1 was added to the polyamic acid solution, and the mixture was stirred for a certain period of time to produce a polyimide composition.

The organic solvent was added so that the solid content concentration of the polyimide precursor solution produced from the reaction was 12.8% by weight to produce a polyimide precursor solution.

The polyimide precursor solution was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor solution was placed in an oven, heated at a rate of 6 ° C./min, and held at 120 ° C. for 10 minutes and 460 ° C. for 55 minutes to proceed with the curing step. After the curing step was completed, the glass substrate was immersed in water to remove the film formed on the glass substrate, and dried in an oven at 100 ° C. to produce a polyimide film having a thickness of 10 μm.

<Example 2> BPDA-pPDA / Compound of Chemical Formula 4 (98.9: 100: 2.2) Polyimide Polymerization The thickness is 10 μm as in Example 1 except that the compound of Chemical Formula 4 is used. A polyimide film was manufactured.

<Comparative Example 1> BPDA-pPDA (98.9: 100) Polyimide Polymerization After filling 100 g of the organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, the temperature of the reactor is raised to 25 ° C. 6.243 g (57.726 mmol) of para-phenylenediamine (p-PDA) was dissolved in the retained state. 16.797 g (57.091 mmol) of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 56.96 g of NMP were added to the p-PDA solution at the same temperature to make a constant amount. After stirring while dissolving for a time, a polyimide precursor was produced.

The organic solvent was added to the polyimide precursor produced from the reaction so that the solid content concentration was 12.8% by weight to produce a polyimide precursor solution.

The polyimide precursor solution was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor solution was placed in an oven, heated at a rate of 6 ° C./min, and held at 120 ° C. for 10 minutes and 460 ° C. for 55 minutes to proceed with the curing step. After the curing step was completed, the glass substrate was immersed in water to remove the film formed on the glass substrate, and dried in an oven at 100 ° C. to produce a polyimide film having a thickness of 10 μm.

<Experimental example 1>
The thermal decomposition temperature (Td 1%), permeability, thermal diffusivity and thermal conductivity were measured for each of the produced polyimide films by the following methods and are shown in Table 1.

<Measurement of pyrolysis temperature>
Using the Discovery TGA of TA instruments, the nitrogen atmosphere, the TGA evaluation progress in the interval of 30 to 00 ° C., and the temperature at which a weight loss of 1% occurred at the initial weight (100%) are shown.
⊚: Td 1% 565 ° C or higher ○: Td 1% 545-564 ° C
X: Td 1% 545 ° C or less

<Transparency>
The transmittance was measured by measuring the average transmittance for a wavelength of 380 to 780 nm with a transmittance meter (model 8453 UV-visible Transmissometer, manufactured by Agilent Technologies) based on JIS K 7105.
⊚: 60% or more ○: 50-60%
X: 50% or less

<Specific heat and density>
The specific heat (J / g · K) of the polyimide film was measured by the DSC method, and the density (g / cm ³ ) was measured by the Archimedes method.

<Heat diffusivity>
The degree of thermal diffusivity was measured using the LFA 467 apparatus of NETZSCH Co., Ltd. shown in FIG. The sample was prepared by cutting a film into a quadrangle having a size of 10 mm × 12.7 mm and depositing gold on both side surfaces of the sample to a thickness of 250 to 500 nm as shown in FIG.

<Thermal conductivity>
The thermal conductivity was calculated by the following formula 1.
[Formula 1]
Thermal conductivity (k) = specific heat (C) x density (ρ) x thermal diffusivity (α)
Table 1 shows the measurement results of Td 1%, transmittance, thermal diffusivity, density, specific gravity and thermal conductivity with respect to the polyimide films produced in Example 1 and Comparative Example.

As shown in the results of Table 1, the polyimide film produced by adding a single molecule of chemical formula 3 has improved specific gravity, density and thermal diffusivity while maintaining thermal decomposition characteristics and permeability, and as a result, It can be seen that the thermal conductivity increased by 2.8 times or more as compared with the comparative example. Therefore, in the polyimide film according to the present invention, the current fluctuation due to the shift of the threshold voltage is suppressed due to the excellent heat dissipation characteristics, and the afterimage problem is solved.

As described above, when a specific part of the content of the present invention is described in detail, those skilled in the art say that such a specific description is merely a desirable embodiment, and the scope of the present invention is not limited by this. The point is clear. Therefore, the substantial scope of the present invention is defined by the following claims and their equivalents.

Claims (9)

A polyimide film containing an imide monomolecular compound as an organic filler and having a thermal conductivity (k) of 0.2 W / m · K or more as defined by the following mathematical formula 1 .
The imide monomolecular compound is one or more selected from the compounds of the following chemical formulas 1 and 2.
The polyimide film contains 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 4,4'-para-phenylenediamine (pPDA) as polymerization components.
[Formula 1]
Thermal conductivity (k) = specific heat (C) x density (ρ) x thermal diffusivity (α)
In Equation 1, C, is ρ and alpha, specific heat of each polyimide film (J / g · K), density (g / cm ³⁾ and the thermal diffusivity a ^(mm 2 / sec) indicates,
[Chemical formula 1]

[Chemical formula 2]

In Formula 1 and Formula 2, X, Y, X ₁ and Y ₁ is a monocyclic or polycyclic aromatic ring or a plurality of monocyclic aromatic rings linked organic group having 6 to 12 carbon atoms .. The polyimide film according to claim 1 , wherein the compound of the chemical formula 1 or the chemical formula 2 is a compound of the following chemical formula 3 or the chemical formula 4.
[Chemical formula 3]

[Chemical formula 4]

.. The mol ratio of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) and 4,4'-para-phenylenediamine (pPDA) is 0.98: 1 to 0.99: 1. The polyimide film according to claim 1 or 2. The polyimide film is measured specific heat 1.5 J / g · K or more at a thickness of 10 [mu] m, density 1.5 g / cm ³ or more, the thermal diffusivity is of claims 1 to 3 is 0.07 mm ² / sec or more The polyimide film according to any one of the items. A polymerization component containing less than 1 mol of 3,3', 4,4'-biphenylcarboxylic acid dianhydride (s-BPDA) with respect to 1 mol of 4,4'-para-phenylenediamine (pPDA) was added to the polymerization solvent. The stage of manufacturing the polyimide precursor and
The step of adding an imide monomolecular compound as an organic filler to the polyimide precursor solution, and
The stage of applying the polyimide precursor solution on the substrate and
The steps of drying and heating the applied polyimide precursor solution, and
A method for producing a polyimide film containing
A method for producing a polyimide film in which the imide monomolecular compound is one or more selected from the compounds of the following chemical formula 1 or chemical formula 2.
[Chemical formula 1]

[Chemical formula 2]

In Formula 1 and Formula 2, X, Y, X ₁ and Y ₁ is a monocyclic or polycyclic aromatic ring or a plurality of monocyclic aromatic rings linked organic group having 6 to 12 carbon atoms .. The method for producing a polyimide film according to claim 5 , wherein the compound of the chemical formula 1 or the chemical formula 2 is a compound of the following chemical formula 3 or the chemical formula 4.
[Chemical formula 3]

[Chemical formula 4]

.. The method for producing a polyimide film according to claim 5 or 6 , wherein the imide monomolecular compound is contained in 0.1 to 10% by weight based on the total weight of the precursor solution. In the curing step through drying and heating of the polyimide precursor solution,
The method for producing a polyimide film according to any one of claims 5 to 7 , wherein the final curing temperature is 450 ° C. or higher. A flexible display device containing the polyimide film according to any one of claims 1 to 4 as a substrate.

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